In manufacturing environments components and assemblies are often transported around the factory floor and between assembly stations using a crane having a hoist suspended from an overhead rail system. While numerous types of bridge cranes and hoists are currently available for lifting and moving objects and parts in and between work stations or cells, a particular problem inherent in these devices is the difficulty an operator encounters in accurately and controllably lifting and translating a load within a work station or between adjacent workstations; in other words enabling an operator to safely perform operations on the product without undo manual exertion, fatigue or injury.
The lifting apparatus of the present invention uniquely overcomes several drawbacks of articulated jib crane devices by providing a lifting apparatus that permits an object to be precisely lifted and moved in a ergonomic manner within or between work stations. For example, parts having an individual weight in excess of U.S. Occupational Safety and Health Administration (OSHA) lifting standards, require a lifting means to transfer the parts into and around the work station. Additionally the same lifting mechanics may be required to reach into machines or freely move the load around obstructions within the work space or a shipping/receiving dock. In order to overcome the limitations of a gantry hoist system or fixed length jib cranes, the current invention includes a free standing lifting device having an articulating jib arm that horizontally traverses or swings about the work space with only a nominal manual effort by the operator. Thus, the “double jointed” jib crane, having two arms attached to one another in one embodiment, provides for a reach zone that substantially encompasses the entire area of the work cell, while allowing movement of the load past obstacles (e.g., posts, columns, machinery) that would prevent rotation of a rigid jib crane with the same swept diameter.
Examples of such systems are found, in various publications by Gorbel, Inc., including its “EASY ARM™ Intelligent Lifting System” brochure (Copyright 2006, Gorbel, Inc.) depicting free-standing and under-hung embodiments; and “ARTICULATING WORK STATION JIB CRANES” (Copyright 2006, Gorbel, Inc.) depicting free-standing, wall-mounted and under-hung embodiments, the contents of both brochures being hereby incorporated by reference in their entirety. Various controls that may be employed in such a system, particularly those relating to the control of the load are disclosed in U.S. patents such as U.S. Pat. Nos. 5,865,426, 5,915,673, 6,299,139, 6,386,513, 6,575,317, 6,622,990, 6,796,447, 6,886,812, D477,901, 7,028,856 and 7,222,839, all of which are also hereby incorporated by reference in their entirety.
In actual practice, however, the implementation of a lifting beam consisting of articulated arms, having a load-bearing cable passing substantially within the rotational junction point of the articulated members, presents to the operator non-uniform, extraneous forces that are counterproductive to a free swinging arm(s) that will also remain in any desired stationary position, hereby referred to as a “put-n-stay” hoist operation. One solution, providing a uniform transitional force, in combination with a retained static position, would be a mechanism to provide a frictional force to resist movement of the jib arms that requires a substantial manual force to overcome the coefficient of friction before the arm(s) is able to be moved. While this approach achieves the objective of “put-n-stay” operation, the understandable limitation of the added work required by the operator to overcome the friction force prior to moving the arm makes such a solution impractical and/or requires means to actuate and release clutches, brakes or the like.
Another solution my include placing the cable/winch assembly at the distal end of the outer most arm, however the weight added to the arm assembly compounds the translation dynamics, and further reduces the load capacity of the arm. Therefore, objectives of the embodiments disclosed herein include, applying minimal uniform force to move, in a horizontal translation, a suspended load that is at rest, and once in motion the object may continue to be moved along a horizontal plane with a generally consistent force from the operator so as to facilitate positioning loads throughout area covered by the hoist or lift. Moreover, once the load is at rest the load should remain at the horizontal position, or “put-n-stay” as indicated above.
Analysis of the disclosed embodiments suggests that there may be at least three contributing factors, in various combinations, that compromise the convenience of an articulated arm having a remotely located actuator or winch (e.g., located on a central, free-standing column or ceiling structure where the articulated arm(s) are anchored as depicted in Gorbel's Easy Arm™ brochure noted above). One adverse force is due to the downward deflection of the arm(s) as a result of the combined bending moment of the articulated arms and the vertical mount of the hoist (e.g., column). This moment is a function of the linear distance of the load from the base mount and results in a force that has a tendency to cause a member to flex or bend In the embodiments disclosed, similar to the Easy Arm™ there are at least two moments. Combined with these moments is a mechanical deflection of the lifting rope or cable arising via connections of the horizontal members and the means by which the rope is passed over the pivot point of the articulated arms.
Ideally, a hoist system, absent any arm droop or deflection (i.e., vertical displacement) and forces that deviate from the centerline of the articulated arms, would only require an operator to overcome the inertia of the suspended load and nominal frictional resistance within the connecting joints between the arms. In reality, droop and other forces are intrinsic in an articulated arm when the winch or actuator is remotely located from the lifting position and where the lifting cable or rope must not constrain movement of the pivot points between the arms. For example, the early Gorbel EasyArm™ as well as the Donati (Model CBB-MBB), Scaglia/Indeva (Liftronic® Series) and Kahlman Produkter AB (QLA Series) are articulated arm lifts having designs that do not result in nearly effortless, uniform movement of the arms over the horizontal range of the lift.
Therefore, in accordance with the embodiments disclosed herein, there is provided a means to counteract, direct and otherwise control the intrinsic forces that prevent or diminish the ability of a conventional articulated arm lift to remain in a put-n-stay position where the forces promoting horizontal movement of a suspended load are essentially in equilibrium.
It is a further objective to facilitate movement of an articulated arm lift in response to a uniform transitional force that is consistently over the entire horizontal range of the lift once the load is in motion. It should be further appreciated that one source of forces tending to impact the uniform movement of the arms, or the put-n-stay operation, is that the lift cable passing over the length of the arms may result in forces tending to prevent movement or to cause movement when an operator releases a suspended load. To eliminate the impact of the cable, a design could be employed wherein the cable passes through the center of any pivot point (e.g., routed around very small pulleys, or actually through longitudinal holes in pivot pins), and thereby does not create the undesirable forces. However, such a design is believed to be impractical for safety, form and cost concerns. Referring briefly to FIG. 1, depicted in a perspective view therein is an exemplary articulated arm lift 20, a Gorbel EasyArm™ lift, having a support column 20 and primary and secondary articulated arms 24 and 28, respectively, connected thereto via pivots. The actuator or winching device 30 is located on the proximal end of primary arm 24, and controls the line or wire rope 36 that is connected to a user control 40 and load 50 suspended from a hook or other end-effector associated with the control.
There are at least two forces that produce the aforementioned objectionable circumstances as a result of the use of a cable guide pulley 32 adjacent to the pivot point 34 between the arms. One such force is the result of “droop” that occurs when a load is applied to the end of the rope 36, thereby creating a moment relative to the column and the position it is attached to the floor. This obviously varies with the location of the load relative to the column, and the height of the column. While moving the secondary (outermost) arm 28 from an in-line position relative to arm 24, the cable moves toward and contacts the pulley, thereby producing a radial force having a tendency to move the secondary arm toward an in-line position with the primary (innermost) arm. Such forces may prevent the secondary arm from remaining in a stationary position. As the secondary arm is pivoted further relative to the primary arm, the cable 36 increasingly becomes wrapped about or engages a pulley 32. Consequently, as the cable wraps about the circumference of the pulley, the moment force increases thereby producing a radial torque between the two arms. In addition, the load 50 is lifted slightly as direct function of the cable being wrapped about the pulley, thereby causing additional work as the suspended load is moved. The combination of the various forces results in a potentially imbalanced condition.
In order to enable a free-swinging, articulated arm lift, where the various interactive forces are reduced or otherwise controlled, the disclosed embodiment contemplate means to counteract or negate the forces that act to prevent movement of the load and/or preclude put-n-stay functionality. The various embodiment disclosed are intended to mitigate or reduce adverse forces that compromise a uniform and sustained effort by the operator to initiate the motion of arm/load, to sustain the arm in motion, and to assure the arm remains in a put-n-stay position when an operator-applied horizontal force to the load 50, or controller 40, is removed. As described below, the embodiments contemplate the use of mechanical cam or similar means to adjust or compensate for such forces.
It is further contemplated that alternative mechanical devices may be employed to achieve the desired operation and to compensate for the forces tending to effect movement of the load about the operating region of the articulated arm lift. Based on the recognition that work is a direct function of load displacement, maintaining a specific load/arm position to counteract reactive forces becomes one objective of the disclosed embodiments. In other words, effectively maintaining the vertical height of the load provides a generally constant potential energy (height) of the load to enable the arms to freely rotate relative to one another through the operating region and to stay in place once the operator stops moving the load; since the load will not be seeking a lowest-height position.
In accordance with one embodiment, a cam follower is situated to be responsive to the lobe of a cam that is positioned at least partly about, or near the pivot point of the lift arm assembly (between the primary and secondary arms), whereby the cam follower progressively modifies the vertical angular elevation of the secondary arm with respect to the primary arm, while the arm is being moved about the operating region of the articulated arms. The technique described herein is advantageous because it provides for an adjusting or compensating force that serves to counterbalance the previously identified inherent forces resulting from loading of the articulated arms and the lift cable or rope passing over pulleys adjacent the pivot points. The improved performance achieved using the combination of a cam and cam follower permits a more uniform manual force to induce and control the traversing of a suspended load attached to the arm. Furthermore, once the load is in motion the sustaining force is maintained by virtue of the varying cam radius associated with the relative radial position between the arms.
This technique is also advantageous because various cam profiles can be readily produced to accommodate a broad range of application specific variables. Therefore, a plurality of alternative cam lobes and configurations could be useful in providing the most appropriate and effective solution in any given situation. It will be further appreciated that the cam may be customized, not only for the typical loading of the articulated arms, but also for a particular workstation, where the operator may wish to have detents (e.g., localized changes such as bumps or divots) within the cam profile for specific arm orientations (relative to the primary arm) where the secondary arm “clicks” into a pre-established location, thereby eliminating overshoot and arm wandering, although an extra effort may required to initially dislocate the arms from such a position and to move a load to another position.
According to one embodiment, there is disclosed a lifting apparatus, comprising: a base; a primary arm pivotally coupled to said base; a secondary arm pivotally coupled to the distal end of said primary arm, thereby permitting free swinging movement of said arms within a generally horizontal plane defined by the primary and secondary arms; an actuator operatively associated with at least one of said arms, said actuator operatively engaging a cable so as to control the height of a load suspended from a free end of the cable beneath the distal end of the secondary arm; and a mechanical adjustment for displacing the second arm relative to the first arm and thereby counterbalance forces acting upon the secondary arm as a result of movement of the load suspended therefrom.
In accordance with a second embodiment, there is disclosed an articulating arm assembly for connecting a lifting device to a load, comprising: a first arm operatively attached to a support at a proximal end thereof and including a pivot pin at a distal end thereof; a second arm having a first member pivotally coupled by said pin to the distal end of said first arm and a second member adjustably coupled to the distal end of said first arm for permitting free swinging movement of said arms relative to one another; a cable between the lifting device and the load that mechanically constrained to pass lengthwise along said first and second arms; and a cam, positioned in proximity to and interposed between the pivot pin and the second member of the second arm, said cam angularly displacing the second member in a vertical direction relative to said first member.
In accordance with yet another embodiment, disclosed herein is a method for controlling the position of an articulated arm lift, comprising: operatively attaching a primary arm to a support at a proximal end thereof, said primary arm including a pivot pin at a distal end thereof; and pivotally coupling, using a pivot pin, a secondary arm to said primary arm to permit free swinging movement of said primary and secondary arms relative to one another, wherein the vertical angle between the primary arm and secondary arm is variably adjustable using a cam positioned in proximity to and interposed between the pivot pin and a portion of the secondary arm, said cam thereby angularly displacing the secondary arm in a vertical direction relative to said primary arm as said arms are horizontally pivoted relative to one another.
Other and further objects, features and advantages will be apparent from a reading of the following specification and by reference to the accompanying drawings forming a part thereof, wherein the examples of the disclosed embodiments are given for the purposes of disclosure.